Re: [PATCH v8 5/5] rust: add dynamic ID pool abstraction for bitmap

[Alice Ryhl]

On Mon, May 19, 2025 at 4:56 PM Boqun Feng <boqun.feng@xxxxxxxxx> wrote:
>
> On Tue, May 20, 2025 at 12:51:07AM +0200, Jann Horn wrote:
> > On Mon, May 19, 2025 at 6:20 PM Burak Emir <bqe@xxxxxxxxxx> wrote:
> > > This is a port of the Binder data structure introduced in commit
> > > 15d9da3f818c ("binder: use bitmap for faster descriptor lookup") to
> > > Rust.
> >
> > Stupid high-level side comment:
> >
> > That commit looks like it changed a simple linear rbtree scan (which
> > is O(n) with slow steps) into a bitmap thing. A more elegant option
> > might have been to use an augmented rbtree, reducing the O(n) rbtree
> > scan to an O(log n) rbtree lookup, just like how finding a free area
>
> I think RBTree::cursor_lower_bound() [1] does exactly what you said

We need the smallest ID without a value, not the smallest ID in use.

Alice